Every once in a while I have a few minutes to review industry research and I visited a terrific resource that I had bookmarked long ago and quickly forgotten. The Journal of Computer-Mediated Communication is a peer-reviewed Internet journal that contains some deep and informative research papers.
To wit, a study released in the January 2006 issue goes into great depth about click habits as they relate to positioning. In short, two experiments demonstrate an increased tendency for visitors to click on the first and the last links in a list.
The entire study, Primacy and Recency Effects on Clicking Behavior is available online and provides some real and credible data to assist in the informational design of Web sites.
Note: Updated on March 11, 2016 for link rot.